Tungsten Alloy

2015-11-27 11:17:07 点击数：

Tungsten alloy, also named tungsten heavy alloy, generally is refractory metal, which has two-phase composites consisting of W-Ni- Fe or W-Ni- Cu or even W-Ni-Cu-Fe, some tungsten alloys are added Co、Mo、Cr, etc. They have very high melting point and have a density twice that of steel and are more than 50% heavier than lead. Tungsten content in conventional heavy alloys varies from 90% to 97% and is the reason for their high density (between 16.5g/cc and 18.75 g/cc). Nickel, iron and copper serve as a binder matrix, which holds the brittle tungsten grains together and which makes tungsten alloys ductile and easy to machine. Nickel-iron is the most popular additive, in a ratio of 7Ni:3Fe or 8Ni:2Fe (weight ratio). The conventional processing route for tungsten heavy alloy includes mixing the desired amount of elemental powders, followed by cold pressing and liquid phase sintering to almost full density.

The matrix alloy melts and take tungsten into solution during liquid phase processing, resulting in a microstructure through large tungsten grains (20-60µm) which are dispersed in the matrix alloy. The as-sintered material is often subjected to thermo mechanical processing by swaging and swaging, which results in increased strength and high hardness. The majority of current usages for WHAs (tungsten heavy alloy) are best satisfied with the W-Ni-Fe system. Alloys such as 93W-4.9Ni-2.1Fe and 95W-4Ni-1Fe represent common compositions. The addition of cobalt to a W-Ni-Fe alloy is a common approach for slight enhancement of both strength and ductility. The presence of cobalt within the alloy provides solid-solution strengthening of the binder and slightly enhanced tungsten-matrix interfacial strength. Cobalt additions of 5% to 15% of the nominal binder weight fraction are the most common.